The relationship between the physiological reaction to a traumatic event and the subsequent development of post-traumatic stress disorder (PTSD) remains obscure and uninvestigated. This project will attempt to clarify this relationship by extending previous work of the PI's and colleagues' performed in chronic PTSD patients to acutely traumatized subjects. This previous work has demonstrated the presence of elevated, poorly habituating physiological responses to the presentation of loud tone stimuli in subjects with chronic PTSD Pilot data from seventeen acute trauma victims studied according to the methodology proposed herein are highly promising for confirmation of the central hypothesis of the proposed work that the presence of large, poorly habituating autonomic and eyeblink responses to loud tones shortly after a traumatic event will predict the PTSD outcome months later. Subject candidates will be recruited from the population of patients presenting to an Israeli University Hospital Emergency Room who have just experienced psychologically traumatic events that meet the DSM-III-R "A" PTSD criterion. At an initial assessment one week following the index traumatic event, the subject's orbicularis oculi electromyogram (EMG), skin conductance, and heart rate responses to a series of loud tone presentations will be measured. At subsequent assessments performed one and six months following the index event, the subject will be evaluated for the presence of PTSD and other mental disorders by means of the Clinician-Administered PTSD Scale (CAPS) and Structured Interview for DSM- III-R (SCID). The tone procedure will be repeated, and subjects will also undergo a further psychophysiological PTSD assessment using a script- driven imagery procedure. A number of PTSD-related and other psychometric measures will also be obtained. The relationship between physiological responses to the tone presentations at the one-week assessment and the PTSD outcome at the one- and six-month assessments will be evaluated by means of logistic regression. A number of other predictor variables, and potentially confounding variables, will be entered into the analysis for the purpose of calculating the adjusted odds ratio for PTSD.